text:
Are engines fed differently in reduced gravity aircraft?
Reduced gravity aircraft are basically airliners without passengers seats. As airliners, those aircraft were not designed to fly for a long time in zero-G. Specifically engines were not designed to be fed with fuel for several tenth of seconds in reduced gravity conditions. I'm aware that aerobatic aircraft are equipped with devices to feed the engine in negative-G conditions for a limited amount of time, but what about the reduced gravity aircraft?
EDIT: aerobatics aircraft are equipped with header tanks and/or flop tube able to get fuel in tank even if flying inverted (e.g. flop tube's end goes to the bottom of the tank, bottom defined in Earth frame of reference, whatever the attitude of the airplane). This design allow pipes to always be inside the liquid fuel of the fuel tank, and thus pumps can do there job (pump liquid). But when in zero G, liquid is no longer attracted toward one side of the tank (either the bottom or other side) and thus pipes may be fed with a mix of air (or whatever gas or vapor that is inside the fuel tank) and liquid fuel. Pressurized tanks do not change this. Yet, engine must be fed in fuel for several tenth of seconds in those condition, and I doubt fuel contained in pipes can last more than few seconds. Devices to fed a reduced gravity aircraft's engine should be different from the one in aerobatics in at least two way:

aerobatics are designed to operate in inverted flight (not zero-G) and are in zero-G condition for a small amount of time (less than a couple of aerobatic maneuvers before being again in normal or inverted flight)
reduced gravity aircraft are airliners (may be modified, but how?)

The two questions are indeed duplicates, but I don't understand why the (7 month-)older is marked a a duplicate of the newer. Chronologically speaking, it should be the opposite, as explained here

The newer question is more specific and seems to have a more authoritative answer. As explained on meta: The general rule is to keep the question with the best collection of answers

@fooot the part of the newer question edited less than 3 hours ago makes both question not duplicates (and explicit why it is not)

@ManuH (or anybody else who can confirm the intent and justify the edit) says "tenth of seconds" a couple of times. In the last paragraph you follow it up with "more than a few seconds". Should this say "tens of seconds" (meaning some number more than 10, but less than 100) or "tenths of a second" (meaning some number less than 1)?

Zero 'g' aircraft are basically commercial aircraft.
In general, it is mainly the fluid systems like the fuel and hydraulic systems in the aircraft which are affected by the zero gravity conditions.
In the case of jet engines, the fuel is transferred by pumps operating under pressure and the fuel injection is also under pressure in the combustion chamber. Consequently, the engine fuel system does not need any modification. In a few aircraft, the fuel tanks themselves are pressurized (like C-5) but this is for safety and wouldn't affect operations.
The engine oil and lubrication system is also usually pressurized and can operate briefly under reduced gravity conditions.
Work done by NASA indicates that aircraft can be used in zero gravity conditions without any major modifications to systems.
The zero 'g' aircraft don't operate in weightless environment for more than 20-30 seconds and the engine systems should be able to cope during that time. The main concern appears to be the training levels of the pilot.

Can you elaborate on the concern about pilot training levels?

OK for the part between the pumps and the engines, but what about the part befor the pumps? Pipes going from the fuel tank to the pump should begin at the bottom of the tanks, in zero-g conditions you cannot garanty fuel is at the bottom of the tank.

The document says the pipes themselves contain enough fuel for 50s, which is more than sufficient. I guess there is some gravity-based gas/liquid separation in each engine and the fuel pump is much faster than what the engine needs. So bubbles may arrive after the zero-g period and are vented. Also, I guess taking fuel from a full tank reduces the risk of bubbles. But as said, just a guess, no definite answer.

There have been several references here at Aviation.SE that fuel is often contained in a collapsible rubber bladder within the wing tank location to prevent the build up of fuel vapor. If that's the case, then the pump sucking fuel out of the bladder would cause the bladder to collapse, no matter the amount of gravity, and that would keep the feed line in constant contact with the fuel contained within.

How would the hydraulic system be affected by zero gravity? Please explain.


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Which civilian airport has the most runways (current and planned)?
I just read Is the airport capacity related to number of runways? . While there are a host of factors, the idea of more runways is obviously so that more flights come in and out. Which is the biggest and baddest airport which has the largest number of people as well as aircraft coming in and out. Few days back I read that the Chinese have some ambitious plan for the Beijing Airport. I do not know how many runaways it would have (the newspaper article didn't tell/share that info.) but would be interested to know which Airport is the king?

@mins - corrected, thank you very much.

Runways may be added to allow operations with wind in multiple directions, so more runways is not the same as more traffic. This military airport (Edwards AFB) has many runways (at least 8). This is where the Shuttle landed when Kennedy Space Center was not possible.

@mins EDW has even 18! (but only 3 of them paved)

Chicago O'Hare International Airport (ORD) today has 8 runways, which is more than any other current airport has. In 2015 14L/32R was closed and 10R/28L was opened, and further runway changes are foreseen.

Beijing Daxing International Airport will be Bejing's third airport (planned to open in September 2019). According to Centreforaviation it will have 9 runways. One runway will be reserved for military use. The ninth runway is not visible on public maps and illustrations at this moment.

Denver International Airport (DEN) currently has 6, but the long term master plan foresees 10 runways in total by 2030, and 12 beyond 2030. See Jonathan Walters' answer for images. (Fun fact: there are a plenty of conspiracy theories about the shape and size of DEN)
Additional runways are not necessarily used to increase (commercial) traffic. Runways maybe reserved for different wind directions, to separate different type of planes (military, general aviation), or for noise abatement. This was already discussed better in the other question that you mention.

As an example for the noise abatement,  this picture (from LVNL) shows a snapshot of active runways at Amsterdam Airport Schiphol. There are 6 runways, of which usually only 2 or 3 are used. The most distant runway (here in green) is almost always in use, causing very long taxi times in favour of reducing the noise exposure of nearby residential areas.

Sheesh, I've heard Schipol had some long taxi times, but I just measured the shortest taxi route from 18R to the nearest terminal ramp entrance and it means 2.75 miles. Maybe they should call an Uber :)

Interesting: O'Hare has 8 runways and handles 76 million people. Heathrow has 2 and handles 74 million. Why the big difference? Does Chicago get lots of smaller flights needing separate runways, or do they just not use all of them due to wind / noise? Or is it simply they have s less dense schedule - a plane per runway every 15 minutes not every 3?

@Tim Chicago definitely gets lots of smaller flights, including a number of regional jets and turboprops. With the cost of a landing slot at Heathrow running tens of millions of dollars, there's a strong economic incentive for airlines to only fly larger aircraft there. See this graph showing significant passenger growth and only modest growth in number of movements. Heathrow also has some restrictions on nighttime flights, which O'Hare has some late flights leaving after 11pm (including a number of cargo operations).

@TomMcW 20-25 minutes for 18R-36L. They at times go pretty darn fast on the taxiway leading there. I've clocked them at 30+ knots on that long taxiway driving on the road parallel to it.

@Tim Take a look at the list of busiest airports by movements. O'Hare has almost twice as many as Heathrow (and Atlanta has even more.) 8 of the top 10 airports by movements (and all of the top 4) are in the U.S. Outside of the U.S., only Haneda (#5) and de Gaulle (#10) make the top 10. That said, Heathrow is in dire need of more runways and has been for quite a while, but space to build them is limited.

Denver International (KDEN) appears to take first place at a total of 12 runways, current and planned.
KDEN currently has 6 runways, with an additional 6 planned. The first four additional runways are planned for completion by 2030, with the last two additional runways planned for completion beyond 2030.

Due to projected growth and Denver's weather patterns, KDEN will ultimately require more runways to serve the same amount of traffic as comparable aerodromes.

Denver International Airport is projected to experience activity levels comparable to those currently at O’Hare and Hartsfield-Jackson Atlanta International Airports. These airports encompass seven and five runways, respectively. O’Hare’s runway system, which is currently undergoing modification, will ultimately consist of six parallel runways providing the ability to simultaneously arrive to three independent runways during poor weather conditions and two crosswind runways. Likewise, Atlanta’s runway system consists of five parallel runways, allowing simultaneous arrivals to three independent runways in poor weather conditions, but without crosswind runway capability. Given the historic wind and weather conditions in Denver, influenced strongly by the Rocky Mountains, crosswind runway capability is critical to maintaining operations during strong winds, poor or marginal weather conditions, protecting the all-weather reliability of the airfield system.

Source
More details including the full airport layout plan (see below) available here.

It looks like a Hakenkreuz.

I guess someone doesn't like this answer. Curious why the downvote? Is there another airport with a current and planned total of runways greater than 12?

Can I upvote the answer & downvote KDEN's plans?  That looks like a headache and a half if they get all of that nonsense built!  And it's not like that place is a breeze to get into & out of now...

@sean, I have rolled back the edits to my answer since my existing wording intentionally addresses the question. There are currently a total of 12 planned runways, including the existing 6.

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text:
What is a circling approach?
What is a circling approach and why is it necessary? I know that if a runway is not suitable for an instrument approach, the pilots should execute landing on a runway which has an instrument approach available.

To add to the above points...
Circling Approaches are used when the Approach you want to use and the runway you want to use are not aligned with each other. Say for instance, you are arriving to the terminal area from the North. The runway you want to use is from the South (probably due to wind). You want to get down to the ground ASAP. You can get cleared to approach the airport using an IAP with a Southbound Final Approach Course. They will also clear you to circle the field in a certain direction. We will use East in this example. You will then get clearance to land on the Northbound (from the south) runway. A play by play would be to:

Follow the full procedure for the IAP with the 180° Final Approach Course.
Once you reach your Circling Minimums, maintain you’re altitude, and turn 30° to 60° to your left.
Turn back to your 180° heading in time to stay no more than 1.3 miles away from the runway surface for Category A aircraft (unless the airport has published alternate circling distances). It would be similar to a (right in this case) downwind leg
Parallel the runway to a point where you can make a normal downwind to base turn.
Start your descent to landing
Land on runway 36

If you never get the runway environment in sight, go missed at the original MAP.
If you lose sight of the runway environment at any time during your circling maneuver, immediately circle back over the runway to fly above it on your missed approach course. And go missed. Remember, the safest place in the airport environment is directly above the center of the runway.
One thing to be aware of on Circling Approaches is that the Circling Minimums are typically below Traffic Pattern Altitude. You will be flying slower and closer to the ground in the airport environment than you are used to. Caution must be exercised.
Also, the Circling Approach does not have to be a complete 180° turn around to land. It could be in any direction.
Finally, some approaches only have Circling as an option. This is due to the approach itself not being aligned with the runway. In the example below, the runway is aligned 179° and 359° magnetic.

Which application are you using for taking this image?  And thanks for expression and illustration

@VolkanEroğlu - This is a screenshot from ForeFlight. You can get similar images from http://www.skyvector.com

A circling approach is executed on an instrument approach procedure which or where the final approach segment is not aligned directly with the runway of intended landing.  Circling approaches can also be flown on instrument approaches where the pilot opts to land on another runway not aligned with the final approach segment, but which has more favorable wind conditions, obstacle clearance, greater landing distance available, or some other characteristic which makes it more desirable to land on.

Even with Sean's edits that last sentence is confusing.  Of course it is ideal to land on a runway with an instrument approach, but when the preferred landing runway is NOT served by an instrument approach, the pilot must follow a procedure to get below the clouds and be able to see to land.
This can be accomplished by radar vectors to a visual approach, but depending on the ceiling, minumum vectoring altitude, and the published approach minimums it may be advantageous to shoot an approach to a runway not in use, and once the runway is in sight, circle to land by maneuvering to join the final portion of the VFR landing pattern.

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text:
What is the purpose of the air inlets on an A320neo's pylon (LEAP-1A)?
What is the purpose of the air inlets on an A320neo's pylon (LEAP-1A)? Passive cooling, air bleed like in the 707, or something else?


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New Research: VGs increase lift to drag ratio up to 880%. Does it work for flaps too?
Aerodynamic Free Lunch: VGs increase L/D ratio up to 880%. Does it work for flaps too?
I understand this research was for a wing without flaps.
I understand this reduction in drag with VGs works only for the alpha range past the max Cl point of the wing without VGs, eg. 8-18 deg, increasing the L/D by 880% at 18 deg AOA as shown in the table and graph below.
Questions:

Would a wing with 20% chord NON-SLOTTED flaps see a similar 84% reduction in drag for each flap setting eg 10,20,30 deg?
Would a wing with 20% chord SLOTTED flaps see a similar 84% reduction in drag for each flap setting eg 10,20,30 deg?
Why does the drag almost stay the same even thought the lift goes up? My intuition is that the VG wing drag value stays close to the 8 deg drag value w/o VGs, as that is the local AOA the wing is seeing due to the VGs, instead of the drag at 18 deg, even though the lift is increasing.  Is that correct?

Article:
Experimental and Numerical Analysis of the Effect of Vortex Generator Height on Vortex Characteristics and Airfoil Aerodynamic Performance
Xinkai Li 1,2,3,* , Ke Yang 1,2,3,4 and Xiaodong Wang 5
1 2 3 4 5
102206, China; wangxd@ncepu.edu.cn
* Correspondence: lixinkai@iet.cn; Tel.: +86-010-8254-3038
Received: 29 January 2019; Accepted: 7 March 2019; Published: 12 March 2019
 Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China; yangke@iet.cn Key Laboratory of Wind Energy Utilization, Chinese Academy of Sciences, Beijing 100190, China
Dalian National Laboratory for Clean Energy, CAS, Beijing 100190, China
Graduate School, University of Chinese Academy of Sciences, Beijing 100049, China
College of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing
 Abstract: To explore the effect of the height of vortex generators (VGs) on the control effect of boundary-layer flow, the vortex characteristics of a plate and the aerodynamic characteristics of an airfoil for VGs were studied by both wind tunnel experiments and numerical methods. Firstly, the ratio of VG height (H) to boundary layer thickness (δ) was studied on a flat plate boundary layer; the values of H are 0.1δ, 0.2δ, 0.5δ, 1.0δ, 1.5δ, and 2.0δ. Results show that the concentrated vortex intensity and VG height present a logarithmic relationship, and vortex intensity is proportional to the average kinetic energy of the fluid in the height range of the VG. Secondly, the effects of height on the aerodynamic performance of airfoils were studied in a wind tunnel using three VGs with H = 0.66δ, 1.0δ, and 1.33δ. The stall angle of the airfoil with and without VGs is 18◦ and 8◦, respectively, so the VGs increase the stall angle by 10◦. The maximum lift coefficient of the airfoil with VGs increases by 48.7% compared with the airfoil without VGs, and the drag coefficient of the airfoil with VGs is 84.9% lower than that of the airfoil without VGs at an angle of attack of 18◦. The maximum lift–drag ratio of the airfoil with VGs is lower than that of the airfoil without VGs, so the VGs do not affect the maximum lift–drag ratio of the airfoil. However, a VG does increase the angle of attack of the best lift–drag ratio.
Source: www.researchgate.net › publication › 331712096

You might want to change the case use of Vg to use all upper case. Or, explicitly spell out Vortex Generator. I came here looking to find out how best glide speed gave you a better L/D ratio.

It might not even work for a different wing. This airfoil is a thick, well cambered airfoil intended for wind turbine blade roots, which are prone to stalling. Impossible to know without doing the analysis and testing.

You do realize that there is no "free lunch" here, right? The only thing the vortex generators are doing is delaying flow separation at the expense of reduced efficiency across the board, as clearly shown in graph (c).

Also, could you link this account to (what I am pretty sure is) your old one?

yes, I accidentally started a new account when I was trying to access the old one, as I think it was only a guest account.  How do I get back to my old account, or better yet, merge the two?

@AEheresupportsMonica All depends what is considered a free lunch and what the mission is. Sticking on a few plastic VGs to increase lift from 1.5 to 2.2 is a pretty cheap way to increase lift, lower landing speed and shorten takeoffs and landings for ultralights flying at low speeds.

@Fred you can message a moderator and ask them for help; they should be able to merge your accounts.

Nothing to see here. Poorly designed or misappropriated airfoils can be improved at some polar point by application of VGs.

Graph C tells the story.  Better to go with slats and flaps.  Vortex Generators remain valuable to alter the airflow characteristics of a section of the airfoil or control surface.
Drag producing and lift destroying chaotic turbulence on the upper rear of the wing appears to be reduced by the Vortex Generators at higher Angle of Attack.  Notice turbulence starts to form before the wing is fully stalled on a "clean" wing, resulting a peak Lift/Drag  of around 6 degrees.  By energizing the air flow and keeping it attached, more lift can be created at higher AOA as seen in Graph A.
However, anything that cannot be retracted will carry a drag penalty at optimum L/D, but, as with many larger radius leading edges, Vortex Generators, or VGs, can make the L/D curve much smoother and predictable rather than a sharp break from a very narrow peak.
VGs have found application in elevators, but a flap beyond a given angle of deflection is actually more useful stalled and draggy.  Lower degrees of flap deflection, along with slats, serve to increase camber of the wing to create more lift at lower speeds, also with a drag penalty compared with "clean".
Note the airfoil used in this study is cambered.  It starts to generate lift a -5 degrees AOA, and drag with VGs is actually greater than "clean" at lower AOA typically found in cruise (Graph B), with little difference in lift produced.

VGs are pretty popular with the STOL ultralight crowd. In fact, Savanahs come factory equipped with VGs instead of slats over the entire wing span, unlike the Zenith 701.

I'm not sure you answered my question. 1. Would VGs reduce drag about 80+% with flaps? 2. Is the low drag due to local AOA being 8 deg, or the energizing of the boundary layer, or a bit of both?

@Fred right!  One prominent writer here calls VGs "poor mans slats", and, as the graphs suggest, certainly would be helpful for STOL.  I would want slats and flaps on a thinner wing for cruise (if I cruised alot).

@Fred drag reduction depends on what AOA you are at.  Notice delaying the onset of "flow separation" with VGs or (or dimples) allows much higher L/D at a higher AOA (and more lift). This might be useful for take-off/climb.  Judging from deltas (are VGs mini deltas?) it may be "energizing" the boundary layer.  The back of the wing (or golf ball) is curving away from the airflow (I'm not seeing "local AOA at 8 deg").


text:
Does runway centerline lighting provide information about distance left before end?
I asked Does runway center lighting increase runway lifetime? and this video was was mentioned.
I don't really understand the significance and I first assumed centreline lighting in night conditions helped crews know half the runway is done and they don't accidentally overshoot the runway.
But I was explained centreline lighting helps in directional and alignment guidance for the aircraft. How is that possible?

OK, you've now asked two questions "Do runways have centreline lighting for reason X?" Why don't you just ask, "Why do runways have centreline lighting?"

I wonder if you wouldn't be interested in reading training documentation, e.g. the Pilot handbook of aeronautical knowledge. Its chapter 14 is about airport operations, and runway lighting starts page 14-18.

Runway centreline lights serve two main purposes:

Inform the pilot about where the centre of the runway is (they are installed on the runway centreline.
Inform the pilot about how far away the end of the runway is (by colour coding the final 900 m metres of runway centre line lights).

Their safety objective is to help prevent misalignments when landing and taking off, as well as to help prevent undershoots and overruns.
They are not always required, and in fact they are considered a complementary system to other visual aids such as runway edge lighting or runway markings, amongst others.

Yes. From wikipedia

Runway centerline lighting system (RCLS) – lights embedded into the surface of the runway at 50 ft (15 m) intervals along the runway centerline on some precision instrument runways. White except the last 900 m (3,000 ft): alternate white and red for next 600 m (1,969 ft) and red for last 300 m (984 ft).

This feature is not unique to centerline lights—runway edge lights are designed the same way—and does not answer the question of the purpose for runway centerline lights, which is primarily providing directional and alignment guidance to the flight crew.

centerline markings (including lights) provide an aiming point for pilots to keep their aircraft properly lined up.
Giving a distance indication is nice, but secondary.

now the way the video shows, it seems the runway with side-lights and the centrelight is a huge 'H' with lights on the left and right-side of the runway and the centreline lighting running in the middle of it. How does it help in directional and alignment guidance ?

@shirish ever tried keeping exact center on the road without a centerline to guide you? Most people tend to end up driving way off center, hugging the left or right marker lines. Same applies to runways, the centerline helps the pilot stay on center, and gives him an aiming point to determine where center is even before he gets to the ground.

Are you possibly confusing the centerline lights which run longitudinally down the runway with either the decision bar or runway end lights that run laterally. The only H-shape I can think of would be if there was a lahso bar running across the runway to indicate the point they need to stop by

My previous comment was notended for the OP. Forgot to tag him

There are special coded red lights for the last 900m of runways.
But not for all. You have to check it before you go.

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text:
Does a 709 ride mean the end of my career?
If I'm required to do a 709 ride following an incident where the plane went off the end of the runway but it wasn't damaged and no one was hurt, what effect does it have on my future as a pilot?
I'm looking to go into commercial aviation (I'm currently a CFI working on hours) and am specifically wondering about how having it in my record will affect interviewing for regionals.

A key question here is why you're doing the ride (if you're willing to share that). Sometimes they're required through no fault of the pilot, e.g. a DPE's performance was found to be questionable.

@sd4356 layman's view here but the question of  why it went off the end of the runway is surely at least as important as the fact that there were no severe consequences.

Depends on the reasons the FAA had to justify the need for a 709 ride.  If it was some kind of bureaucratic maneuver without justification for doing so and you pass the ride with flying colors, probably nothing.  If there was a serious discrepancy in your airmanship which required a 709 ride to verify improvement on your part, it's going to depend on whether it was a one time event or a trend in airmanship deficiency resulting in the check ride.  In addition have there been further reports of deficiency in your airmanship after the 709 ride?  That will also have an effect on an employer's judgment of you as a potential employee.
Whatever the reasons for the 709 ride, an employer is going to see it, so be prepared to explain anything associated with it.
Look at this from the employer's perspective:  I'm going to put you in charge of a big, heavy multimillion dollar machine that you are going to pilot several miles off the ground at speeds close to that of sound.  If anything goes wrong, you're going to get killed, someone else on board is going to get killed, people on the ground are going to get killed and I'm going to get sued, go bankrupt, end up in jail, or all three if your negligence can be traced back to me.  Is there anything in your background which make me suspicious this is likely to happen if you are in my employ as a pilot?
The fact that you do make mistakes, possibly even serious ones, is not necessarily the issue here; everybody makes mistakes.  The last time you flew on an airliner the flight crew probably screwed something up.  People with thousands of PIC hours learn something new on their next flight and it's a mark of a good pilot that you can identify your own faults and fix them.  The Blue Angels have a private saying amongst themselves that "We've never flown a perfect airshow and we probably never will.  But we strive for the perfect airshow each and every flight".  Striving for perfection as a personal motivator is the mark of a good airman and looks good on a resume, no matter how balls up some flight in your logbook was.
The real issue here is do you have a recent or chronic history of uncorrected gross negligence or inability to handle the kinds of aircraft a potential employer flies which raises red flags as to your airmanship or trustworthiness.  If you have a spotty record or recent 709 ride in your recent past, take a couple of years staying on with your current employer and do an outstanding job.  Work on your airmanship and develop a stellar reputation with them as a pilot.  That will go a long way to erasing the past, or at least mute its bite.
Speaking of trustworthiness, DO NOT LIE TO A PROSPECTIVE EMPLOYER ABOUT A 709 RIDE OR ANY OTHER FAILED CHECKRIDE.  Aviation is built upon an honor system and any kind of detected lying or deceitfulness on your part is an automatic fail with no second chances, no matter how squeaky clean your career is up to that point.  If they ask about it, tell it like it was, no more, no less, and let the chips fall where they may.  It will yield the best possible outcomes, even if you don't get the job.

I agree with @Carlo on this, the best thing you can do is focus on passing the 709 ride and showing good airmanship afterwards to improve your record. No need to be defensive about it, in fact do a self-analysis and see where you can improve.

TIL the phrase "let the chips fall where they may" ...

@kmonsoor: Agree. Carlo's is the kind of English I love to read as a way to strive for perfection in mine...

Thanks! All very helpful. I don't have any recent or chronic history of gross negligence or inability to handle the aircraft I currently fly. Unfortunately, I was in a situation where I had to make a decision and choose the lesser of two evils resulting in the incident. Additionally, I have no issue taking responsibility for what happened or explaining it in an interview, I just don't want this checkride on my record to be a career ender. I appreciate your detailed response.

A 49 U.S.C. 44709 ride is typically given when the FAA has reason to believe the applicant does not have the minimum pilot standards for their certificate or rating.
As Pondlife pointed out, this can be because of a deficiency with the DPE that administered the practical test or because of an accident or incident after you passed the practical test.  It is also quite possible to get a 709 ride when you have broken the regulations, airspace infractions or other procedural things.  Typically the FAA will mitigate this risk with their compliance philosophy where they want to help weaker pilots maintain and improve their piloting capabilities.
I agree with Carlo that most airlines will see the 709 ride and ask questions.  How you respond to those questions will determine your aviation career.


text:
Why are propeller driven aircraft commonly built with a higher wing aspect ratio and a straighter wing angle?
Why do propeller driven aircraft (especially smaller ones like fighters) tend to have a narrower wing with a higher aspect ratio and a more perpendicular wing angle in relation to the body, whereas jet powered aircraft have a broader wing with a lower aspect ratio (a more "delta" shape) and also more angled? Does it have something to do with the operating speed and aerodynamics?

Note that a lot of smaller jet aircraft also have straight wings (examples: Yak-40, Do 328J, Learjet 25).

Yes it does. The reasons are many, and complicated, but I will try to briefly summarize them here in simple terms.
A jet-powered fighter has to pop through the sound barrier with minimum ill effect and be aerodynamically predictable at supersonic speeds. It also has to withstand the great stresses associated with these actions and those imposed by high-G maneuvering, without failure. All these thing argue in favor of stubby and sharply swept wings that are either trapezoidal or delta-shaped.
I invite the experts here to add to this list and to perhaps offer more technical background.

Speed is the reigning factor here, and aerodynamics as well of course.

Speed.
Propeller driven aeroplanes operate at lower speeds than jet engines - propellers are more efficient until compressibility effects start to appear, and it is these same compressibility effects that influence the wing shape as well. Compressibility as in: give air enough time to move out of the way and follow the wing contour. Usually, propeller aeroplanes operate in this aerodynamically docile speed regime.
Aerodynamics.
A wing creates lift by deflecting air downwards, and is most efficient if there is a large amount of air deflected a bit: the least induced drag is created. So the wingspan is the most important parameter here. Lower speed aeroplanes will stick their wings straight out, as much as possible without creating large structural issues due to wing root bending loads becoming unmanageable.
Aerodynamics at higher speed.
Once shock waves start to appear, drag rises rapidly. But only the air flowing perpendicular to span concerns us for the lift creation, and therefore we can present the wing at an angle and use the lower perpendicular speed component for lift creation. But swept wings create many more structural problems than straight wings, and also since we're going faster already the argument of more air at less deflection speed is of less relevance. We have many more problems to tackle here than only minimise induced drag.

It's not simply a matter of jet vs propellor, either.  It's fairly easy to find subsonic jets - early fighters, trainers, bizjet - with a more straight & narrow wing.  Also consider the various "swing-wing" designs...

@jamesqf: The early straight-winged jets were the result of sticking to what is known. Witness the F-84 which mutated from a straight to a swept wing when Republic got comfortable with designing swept wings.

Another factor is stability: A stubby wing has more torsional stiffness and shifts divergence speed up. So again, it is about higher speed for jets vs. propellers.

@Peter Kämpf: Then there are others, like the T-37, that stayed with straight wings over a long lifespan.  Probably because it had a relatively low top speed: https://en.wikipedia.org/wiki/Cessna_T-37_Tweet

@jamesqf: I would count the Cessna T-37 firmly within the early jets. Cessna had no experience with swept wings whatsoever at that time and the requirement did not call for them, also.

@Peter Kämpf: Why didn't the requirement call for swept wings?  Perhaps because it didn't require a high speed?  You see this in other jets, like some of the Citation business jets, or the A-10 Warthog, that fly at comparatively low speeds.


text:
Why is the empennage design of this Lockheed 1049E so complicated?

Photo.
What is the reason for making the empennage of this Lockheed L-1049E Super Constellation's design look so complicated with two vertical horizontal stabilizers? In my understanding, the more components installed, the more the weight of the airplane will be, and as a result will put more load on the engines, especially if there will be more actuators required. Do all the horizontal stabilizers have controllable surfaces? What is the reason for making the horizontal and the vertical cross each other, and not attaching them at their tips (marked with yellow and green circle)?
Edit: I corrected the question on the body from with two additional horizontal stabilizers? to become with two additional vertical stabilizers? as supposed to be as I marked in the picture.

"... with two additional horizontal stabilizers?" - I'm guessing you mean vertical stabilizers? The airplane in the picture has three vertical (yaw) stabilizers, but only one horizontal (pitch) stabilizer.

Additional related question; "wouldn't the design of this tail have generated less interference drag if the vertical stabilizers had been placed at the very ends of the horizontal stabilizer, with no curved "tips" of the horizontal stabilizer extending outboard of the vertical stabilizers?   (And note that the same question may be asked of the Lockheed P-8 Lightning.)  Similarly, wouldn't it also have been beneficial to eliminate the middle vertical stabilizer and enlarge the outboard ones as needed?"

They weren't affected by the Area Rule, but they were by  the Rule of Cool.

@TimberSwett, many thanks for your correction. I corrected it. Yes, it supposed to be vertical stabilizer.

@quietflyer, that also my intention to put "complicated" on the title and marked both the extended part of the stabilizer, both the outboard horizontal stabilizer and the vertical stabilizer. I hope our friend will have the answer. Here is a clear picture the empennage of Antonov An-225, clearly shown it no horizontal extension from the ourboard vertical stabilizer, but yes it is there are extention to beneath the horizontal stabilizer. So, my question become more significant to be answered.

@quietflyer: Your last suggestion would have rendered the Constellation's tail too tall to fit in many of the hangars it inherited from earlier, smaller airliners.  They spread the surface out over three tails in order to make them low enough to fit.

Complicated is a matter of opinion and I wont address that specifically since its somewhat subjective. But the core of the question is "why did the L-1049E have 3 tails" which is a legitimate question for this site.
The design was to allow the aircraft to fit in hangars of the time

A sleek fuselage, something like an elongated fish with smooth curves,
  featuring a circular cross-section, a snub nose, and a triple-fin
  tail. Triple tailfins were selected because a single tailfin would
  have been too tall to fit into typical hangars.

The L-1049E had tricycle style gear that was quite tall (for the time) and a standard single tail would have made the aircraft too large to fit into the hangars that most fields had.
The above link also discusses that for a particular Military version ("WV-1") of the aircraft the lower section of the tails were extended to compensate for a radome being mounted on the top. This came along only a year into the design and the subsequent builds may have been a hold over.
Weight as a result of the added rudders would not have been as much as you may expect since they were traditional fabric covered style surfaces

Triple tailfins were selected because a single tailfin would have been too tall to fit into typical hangars. Not due to an aerodynamic reason. Interesting.

Well, an aerodynamic reason, in that the amount of fin/rudder area required dictated how tall a single tail would have been.  Think B-17 or B-29 class -- but the B-17 was a tail dragger.  Add tall tricycle gear, and that tail is much higher above ground.  The military had to modify a lot of hangars for the B-29 -- commercial couldn't just throw money at the hangaring issue.

But there are another question, are all the horizontal stabilizers have controllable? and What is the intention to make the horizontal and the vertical crossed one each other, and not put on the tip of both (marked with yellow and green circle)? The second question at least, I don't think it due to hangar limitation. Is any aerodynamic reason for that?

@ZeissIkon, The military had to modify a lot of hangars for the B-29 -- commercial couldn't just throw money at the hangaring issue. This is make sense.

Ideally you would extend the vertical tail equally above and below the horizontal surface, which would allow the T junction to be a bit lighter since it doesn't have to absorb major bending into the base of the T.  Problem is now the bottom of the vertical fin sticks down too much to clear the ground when rotating for takeoff or when landing.  So you have to raise it and make the intersection beefy enough.  Engineering is a Wack-A-Mole https://en.wikipedia.org/wiki/Whac-A-Mole game, where, when I whack the mole that pops up in this hole, it pops up in another hole and on and on it goes.

@JohnK, interesting. If I compare to Antonov An-225's tail, your comment is likely true. I said likely as I don't have competency to say it is true or not. We may compare also to some modern airplane which the winglets are "terminated" in Y-shape rather than bended up as many other. We may see it in Airbus A380.

The reason the landing gear was so tall is because they used large engines with large diameter propellers. The gear had to be tall for the props to clear the ground.

@AirCraftLover Look up "shuttle carrier 747" and how it's tail is different from a regular 747. It's because the shuttle mounted on top disrupts center fin. An-225 was designed to carry Buran from beginning, that's why it has 2. I've read somewhere that the second unit was supposed to have usual tail with one big vertical stabilizer. Winglets are not comparable to a tail fin, they're not meant to carry loads. BTW, horizontal stabilizers on Super Constellation are "not controllable" at all. Only elevators and rudders move. You want stabilator, this is not.

As another data point for twin tails, the B-24 famously had a twin tail that was converted to single tail in follow-up models. Both the PB4Y and a large B-24 order cancelled due to the end of the war had single tails because they improved stability over the twin-tailed model.

All vertical fins had a controllable rudder as can be seen in this photo. -although that is actually a L-049, I think the rudder system is the same.

@TomMcW: As far as I know, the Constellation's flight controls stayed the same throughout the entire series, yes.

@TomMcW, many thanks for the clear picture. A picture explains more than thousand words.

With respect to many contributors, I have to accept this answer. I understand that credit will go to @dave, but however, his comment trigger another completing comment.

Food for thought: perhaps the design of the Constellation's tail was inherited -- aesthetically if not engineering-wise-- from the Lockheed P-38 Lightning, where the position of the two vertical fins was selected to put them in the optimal position relative to the propwash from the two engines.  Even on the P-38, it seems it might have been possible to generate an equally effective tail with less interference drag by rearranging proportions and positions of the various surfaces to eliminate the little "stub" ends of the horizontal tail that projected outboard of the vertical fins, for a tail design more like that of the P-61 Black Widow.  With the four-motored Constellation, it seems that it would have been an even simpler matter to select proportions of the tail surfaces such that the vertical fins could have served as "end plates" for the horizontal tail, with no projecting "stub ends" outboard of the vertical fins, thus reducing interference drag.  It would also seem that interference drag might have been further reduced, while still meeting other design goals, by selecting a tail design with two vertical fins rather than three.

No it was just have hangar door clearance with the necessary surface area because the airplane was being designed with private airline hangars of the day in mind.   Otherwise a single tail would have been a no-brainer, as it is on 99% of other designs.

The intent of my answer was not to addess why a multi- fin design was chosen, but rather why that particular multi-fin design was chosen.

Roger.. Don't exclude a little bit of "styling" in the mix.  Designers have few areas where artistic expression can trump aerodynamic necessity (although one of the beautiful things about aviation is the happy coincidence that aerodynamic necessity and artistic beauty are in harmony more often than not).  Vertical fin shapes and related factors are one of the few places that a designer can make an airplane distinctive from a purely styling perspective.


text:
Is it possible to convert a passenger A380 to carry cargo?
I heard an expert say that one of the A380's weaknesses is that it only comes in a passenger version, not a cargo one like the B747 does. The cargo version of the B747 makes its market wider. One more weakness of very large jumbo jets (A380 and B747) is that, nowadays, most flights fly directly to the destination (point-to-point), not hub-to-hub as in the 1970s. The point-to-point model causes airlines to make more frequent flights with smaller aircraft. In my country, even small airports are now international airports. Two neighbouring cities in neighbouring countries have small propeller aircraft flying directly between them, without having to go through the main airport in one country's capital city. This makes it very clear that very large jumbo jets are no longer required for passenger service.
On the other hand, the demand for air cargo has never been greater. Trade over the globe has to be quicker. This means that large jumbo jets are needed in cargo service, and - to allow easy centralization of cargo-handling equipment and personnel - it's generally preferable for these freighters to operate to and from the largest, most central airports in a country.
The question is, is it possible to convert an A380 for cargo service when there is no longer a market for the passenger version?

Thank you @sean have edited this question. You made it more understandable.

Also note one of the key reasons people like the 747-8F is that the nose of the airplane can swing up and allow you to load stuff directly in. The 380 would not be able to do that

That I heard that since the begining, Boeing has designed the airplane for cargo anticipate the market.

it was my understanding that they figured that Concorde and similar SSTS would take over the long haul passenger market, so they built the 747 to be a good freighter

Airbus originally planned on a freighter version and UPS and FedEx both ordered some of them. Production delays with the passenger version resulted in the freighter version being delayed and both of them canceling their orders.
The main issue why there is no freighter version is that the internal volume of the aircraft is too large to make it economical for cargo operations. I.e. the density of the cargo generally is too high to take advantage of the full internal volume before hitting the aircraft's maximum take-off weight. As a result, you end up hauling a whole lot of "extra airplane" around. The only time that extra volume is useful is for really low-density cargo loads.
That extra internal volume is useful if you have to move a large number of passengers into slot-constrained hub airport like London Heathrow or JFK but packages don't care much about personal space...
In words other than mine:

An A380-F would be too fat to fly at a profit: The plane would hit the maximum payload (a constraint of weight) before its maximum cubic space (a constraint of volume). Its design can’t support the maximum payload required to generate a profit.

Here are some good other more in-depth analyses.
Something that was surprising to me initially was the amount of modifications that are necessary to convert a passenger aircraft to a cargo aircraft. This paper from a Bedeck Aviation Group (Boeing affiliated passenger to cargo conversion house) provides a good breakdown of the steps required for a 767 conversion. This video from Boeing provides a good visual summary as well (music and hair styles are an added bonus).

So, can I say that, almost no chance to convert it?

That's what I would speculate. Even if the money would be available to do the conversion tasks (such as main floor reinforcements), it is questionable it would ever be economically viable.

Very interesting to see the fate of the King of the sky.

It very much depends on the type of cargo, which the linked article doesn't distinguish. Package freight companies, like UPS and FedEx ship things like Amazon boxes which are mostly air and have much lower density than say bulk car parts. Though the linked article makes a big fuss about the mass capabilities of the 747F, there's a reason why FedEx doesn't fly it: too much mass capability for volume. This is exactly why UPS and FedEx ordered the A380F, the volume made sense for their missions.

@user71659 - Agreed. But since the majority of cargo (at least today) is the e-commerce driven, lightweight package freight, demand for an A380F would likely not be very strong. That is not to say that there aren't applications where an A380F would make sense; its just not the majority of the wide-body freighter market. And that, in turn, makes the business case for the initial investment required for the conversion hard to close.

I got scared when they cut the hull of the 757.

Another queston is probably if the typical fraight airports (often not the same as the big passenger hubs) could even accomondate the A380. Infrastructure for loading, unloading and fueling the aircraft could be built for sure. But could the taxiways and runways andle the A380?

It would certainly be physically possible to do so.  The open question is how much it would cost and how much it's worth to carriers.
Airbus did promote the A380F Freighter as a possible application, and it was available for orders at one point.
However, while the aircraft has much more volume than others (like a 747), it does not lift proportionally that much more weight.  So the market appears to be limited to package carriers which have lighter cargo.  The folks carrying heavy stuff wouldn't be able to fill the plane.  Both FedEx and UPS placed orders for it.
Airbus stopped work on the project to dedicate more resources to the passenger variant.  The delays meant that the original orders were cancelled when no firm date could be given to the airlines for delivery.  Wikipedia says that the option was removed from the Airbus webpage in 2015.  Presumably if there were sufficient interest from airlines, the option would have been funded.
There's also the question of how you'd load the upper deck.  A carrier would want to have cargo lift equipment that could put items there.  That might be expensive to develop/obtain unless you're going to be running lots of planes and makes it harder to bring one in without the prospect of adding many more in the future.
Traditionally cargo carriers have been able to use older equipment that has been retired from passenger use.  I suspect that some will eventually be converted, but that's pure speculation on my part.


text:
Can an Airbus A380 or Boeing B747 fly with only 2 engines?
What would happen if, during cruise at a high gross weight, one of these airplanes suffered a double engine failure:

With one failed engine on each side (leaving one working engine on each wing)?
With both failed engines on the same side (leaving the aircraft with two working engines on the left wing and none on the right wing, or vice versa)?

I know that airplanes with two engines can still fly with only one working engine (by using the rudder to counter the yawing moment created by asymmetric engine thrust, placing the aircraft into a sideslip).

I have a sneaking suspicion @Terry (a user on here) will be able to answer for the early 747 variants. Hopefully he sees this one.

There should be no reason why they can't - any airplane can manage on 50% of thrust, but as with a twin jet with a single engine failure, half power isn't enough to keep cruising at 37000 ft and they'll have to descend to a lower altitude.  It's done at a speed that gives the lowest descent rate and is known as a "driftdown".

@JohnK No, it's done the other way. You only assume a single engine failure, regardless of how many engines the plane has. If a plane needs x thrust to fly safely at some mass, and has n engines, then they put in engines with x/(n-1) thrust. This is why the A340 is famously lethargic, it has less of a margin over minimum thrust. It's also why the BAe 146 has 4 engines, the short-field performance is based on 3/4 of maximum thrust, not 1/2.

I realize the the performance assumptions are single point of failure not double, for the purpose of climb and altitude performance, just saying that a 4 engine jet should be able to stay in the air at some altitude on 2, like a piston twin can stay in the air on half its power but can barely climb.  On the other hand, with the thrust line with 2 on one side running so far outboard, maybe there isn't enough rudder authority?

A single engine failure in a 4-engine aircraft is an "event" but not an emergency. A 2 engine failure is an emergency and the pilots will put the aircraft down at the earliest  opportunity. Even a 2-engine out on one wing isn't an "unflyable" aircraft, but they aren't going to continue on with 2 engines out. USA Today "Ask a pilot" 2 engine failure and 747 2 engine crash

You might want to compare El Al 1862. That flight had other problems, but it did remain flyable with two out of four engines not just inoperative, but actually broken away together with a significant portion of the leading edge of one wing. (Their problem was that they couldn't land.)

@user71659: No, the certification requirements for more-than-two-engined aircraft include the ability to maintain flight with two engines failed.

@Sean That says it doesn't swerve out of control, not be able to climb or even maintain level flight. What that requirement does is to set minimum control speeds after an engine failure, e.g. OEI approaches may require a higher speed to maintain rudder authority. The requirement to maintain a required climb gradient is specified with only a single engine inoperative (Part 25.121).

@aCVn: It should be noted that, although this wasn't the case in that particular instance, an engine or engines breaking away cleanly would actually give better performance than a simple engine failure or failures would, since you no longer have the huge windmilling drag bucket(s) hanging off the wing(s).

First, my experience was with 747-100/200 aircraft. However, I'm reasonably certain that the subsequent variants of the 747 would perform just as well, and I would be surprised if the A380 did not as well.

If during cruising with full load....

"Full load" is a little ambiguous. If what is meant is MTOW (max takeoff weight), note that by the time you reach cruising altitude, you're considerably lighter than MTOW.
But let's say you leveled at FL310 or thereabouts, and shortly thereafter two engines failed. Discounting catastrophic failures that leave things hanging out in the wind that generate a lot more drag than a simple inoperative windmilling engine, you should be able to fly as far as your fuel will take you, although common sense and the regulations would dictate finding the nearest suitable airport.
You won't be able to maintain your 4-engine cruising altitude. You'll drift down until you reach an altitude that you can maintain.
You'll be able to fly whether the two failures are both on one side or one on each side, but both on one side is the more problematical. We used to practice that in the sim. They always put both failures on one side to make it more interesting. The drag from the rudder necessary to counter the adverse yaw from the operating engines is significant, and as you start reducing the power for the landing, judging how much rudder to decrease and when is an interesting dance. You would have run in lots (maybe all) the rudder trim. How much of it should you take out and when. Take it all out too soon and your leg is going to get awfully tired.
While a double failure at cruise is handleable, it's easy to come up with scenarios that are not. If you had a double failure on takeoff just after V1, I doubt you'll make it. V1 and the balanced field length are predicated on one engine failing, not two.
Take a look at https://thepointsguy.com/2017/03/engines-boeing-a-747-can-fly-on/, the relevant part is:

After almost 15 minutes in a controlled gliding descent, the crew coaxed one engine back to life, allowing them to significantly reduce their rate of descent. A few minutes later, a second engine came back on line with partial power, allowing the aircraft to enter a slow climb.

It's also worth noting, I think, that when you're doing a 3-engine ferry in a 747, you're depending on it being able to continue flying on two in case of an engine failure during that ferry flight.
A final thought about the last part of your question:

controlling the rudder makes the airplane fly sideway.

To the best of my knowledge, the use of the proper amount of rudder to counter asymmetrical thrust does not make the airplane fly sideways. However, I am not an aerodynamicist. Perhaps one of the many here qualified in that area can comment.

You are right; with full rudder the aircraft will most likely fly at some sideslip angle, but still mostly ahead. The side force from the rudder needs to be balanced somehow, and the only effective surfaces that can do that are the wing (shallow bank, wing with live engines low) and the fuselage (in a sideslip). Since you get more yawing moment from the rudder when flying with some bank angle, I would expect that with two dead engines on one wing only banked flight will be trimmable.

"Full Load" mean that the aircraft is loaded at maximum load minus the consumed fuel. Or another word, when the airplane is loaded approaching their load.

Perhaps the best wording is sideslip as @PeterKämpf said.

Terry already provided the practical side! A similar question was asked already, regarding the Airbus A380. Thanks to DeltaLima:
https://aviation.stackexchange.com/a/11583/1084
Basically it is a requirement for certification, that a B747, A380 or A340 is still flyable with two engines off.


text:
Who authorizes low visibility takeoff operations for airlines, and what is required?
A previous question pondered the legality and safety of low visibility Part 91 takeoffs. I am wondering about the requirements for low visibility takeoff for commercial airline operators (e.g. Part-121 scheduled operations). I know of authorizations for operators down to 600 RVR (though I believe I recall 300 RVR for one carrier out of DEN), and various requirements for other increments below standard takeoff minima.
My question is:

Which RVR are authorized and what ground equipment requirements need to be met to use them?
What authorizes (regulation? op spec?) these reduced visibility operations?

AOM should be diversified
ie navigational and Meteorological DATA ,for each runway example for Meteorology RWY 17 OF ENTEBBE specification for RVR AND CELING for different aircrafts like Helicopters, 1-2 engine A/CS, FOR LARGER AIR CRAFTS

The Part 121 regulation that governs low visibility takeoffs are specified in 14 CFR 121.651.  It references company OpSpecs and 91.175 and Part 97:

"Standard" takeoff minimums are specified in 14 CFR 91.175 and would be the highest of:

Non-standard takeoff minimums specified on the airport charts (FAR 97)
For aircraft, other than helicopters, having two engines or less — 1 statute mile visibility.
For aircraft having more than two engines — 1⁄2 statute mile visibility.
For helicopters — 1⁄2 statute mile visibility.

OpSpec C056 is issued to all 121 carriers, and basically just spells out the "standard" takeoff minimums that I listed above, and specifies that RVR must be used if it is available on the runway.

OpSpec C078 is normally issued and allows taking off with lower than standard visibility as long as the airport doesn't already have published higher than standard takeoff minimums.  This is a fairly involved OpSpec with several optional paragraphs, and operators may be approved for takeoff operations down to and including 300 RVR.  For those not familiar with the term, RVR (Runway Visual Range) is the distance that a pilot can see down the runway, measured by automatic equipment,  and is measured in feet in the US.
It offers approvals for the following visibilities:

1/4 SM / RVR 1600:

Touchdown zone RVR (or mid RVR if touchdown zone is inop) is controlling:
Requires "runway markings or runway lighting provide pilots with adequate visual reference to continuously identify the takeoff surface and maintain directional control throughout the takeoff run." (Basically as long as the pilot feels comfortable, but specifically mentions HIRL, CL, and RCLM as okay.)

RVR 1000 (optional)

Touchdown zone RVR and rollout RVR (A mid-RVR report may be substituted for either if they are inop, but still must have two systems) are both controlling
Requires Runway Centerline Lights (CL)

RVR 500 (optional)

Touchdown zone RVR, mid RVR, and rollout RVR are all controlling (one may be inop)
Requires Operative runway centerline lights (CL)
Requires Runway centerline markings (RCLM)

RVR 300 (optional)

Requires a takeoff guidance system
Requires operative high intensity runway lights (HIRL)
Requires operative runway centerline lights (CL)
Requires serviceable runway centerline markings (RCLM)
Front course guidance from the localizer (if applicable to the system used)
Crosswind less than 10 knots
Touchdown zone RVR, mid RVR, and rollout RVR are all controlling (one may be inop)
Requires special training requirements for both the PIC and SIC
Taxiways with operative taxiway centerline lighting must be available

Regulations/Sample OpSpecs

§121.651 Takeoff and landing weather minimums: IFR: All certificate
  holders.
(a) Notwithstanding any clearance from ATC, no pilot may begin a
  takeoff in an airplane under IFR when the weather conditions reported
  by the U.S. National Weather Service, a source approved by that
  Service, or a source approved by the Administrator, are less than
  those specified in—
(1) The certificate holder's operations specifications; or
(2) Parts 91 and 97 of this chapter, if the certificate holder's
  operations specifications do not specify takeoff minimums for the
  airport.
§91.175 Takeoff and landing under IFR.
...
(f) Civil airport takeoff minimums. This paragraph applies to persons
  operating an aircraft under part 121, 125, 129, or 135 of this
  chapter.
(1) Unless otherwise authorized by the FAA, no pilot may takeoff from
  a civil airport under IFR unless the weather conditions at time of
  takeoff are at or above the weather minimums for IFR takeoff
  prescribed for that airport under part 97 of this chapter.
(2) If takeoff weather minimums are not prescribed under part 97 of
  this chapter for a particular airport, the following weather minimums
  apply to takeoffs under IFR:
(i) For aircraft, other than helicopters, having two engines or less—1
  statute mile visibility.
(ii) For aircraft having more than two engines—1⁄2 statute mile
  visibility.
(iii) For helicopters—1⁄2 statute mile visibility.
C056, IFR Takeoff Minimums, Part 121 Airplane Operations - All
  Airports.
a. Standard takeoff minimums are defined as 1 statute mile visibility
  or RVR 5000 for airplanes having 2 engines or less and ½ statute mile
  visibility or RVR 2400 for airplanes having more than 2 engines.
b. RVR reports, when available for a particular runway, shall be used
  for all takeoff operations on that runway. All takeoff operations,
  based on RVR, must use RVR reports from the locations along the runway
  specified in this paragraph.
c. When a takeoff minimum is not published, the certificate holder may
  use the applicable standard takeoff minimum and any lower than
  standard takeoff minimums authorized by these operations
  specifications. When standard takeoff minimums or greater are used,
  the Touchdown Zone RVR report, if available, is controlling.
d. When a published takeoff minimum is greater than the applicable
  standard takeoff minimum and an alternate procedure (such as a minimum
  climb gradient compatible with aircraft capabilities) is not
  prescribed, the certificate holder shall not use a takeoff minimum
  lower than the published minimum. The Touchdown Zone RVR report, if
  available, is controlling.
C078, IFR Lower Than Standard Takeoff Minimums, 14 CFR Part 121 Airplane Operations - All Airports.
Standard takeoff minimums are authorized in operations specification
  paragraph C056. The certificate holder is authorized to use lower than
  standard takeoff minimums in accordance with the limitations and
  provisions of this operations specification as follows.
a. Runway visual range (RVR) reports, when available for a particular
  runway, shall be used for all takeoff operations on that runway. All
  takeoff operations, based on RVR, must use RVR reports from the
  locations along the runway specified in this paragraph.
b. When takeoff minimums are equal to or less than the applicable
  standard takeoff minimum, the certificate holder is authorized to use
  the lower than standard takeoff minimums described below:
(1) Visibility or runway visual value (RVV) ¼ statute mile or
  touchdown zone RVR 1600, provided at least one of the following visual
  aids is available. The touchdown zone RVR report, if available, is
  controlling. The mid RVR report may be substituted for the touchdown
  zone RVR report if the touchdown zone RVR report is not available.
(a) Operative high intensity runway lights (HIRL).
(b) Operative runway centerline lights (CL).
(c) Serviceable runway centerline marking (RCLM).
(d) In circumstances when none of the above visual aids are available,
  visibility or RVV ¼ statute mile may still be used, provided other
  runway markings or runway lighting provide pilots with adequate visual
  reference to continuously identify the takeoff surface and maintain
  directional control throughout the takeoff run.
[NOTE: If an operator is not authorized RVR 1000 the POI will not
  select RVR 1000 in the OPSS. If the OPSS is not available the POI
  should delete subparagraph b(2), b(3), & b(4) from the word
  boilerplate.]
(2) Touchdown zone RVR 1000 (beginning of takeoff run) and rollout RVR
  1000, provided all of the following visual aids and RVR equipment are
  available.
(a) Operative runway centerline lights (CL).
(b) Two operative RVR reporting systems serving the runway to be used,
  both of which are required and controlling. A mid-RVR report may be
  substituted for either a touchdown zone RVR report if a touchdown zone
  report is not available or a rollout RVR report if a rollout RVR
  report is not available.
[NOTE: If an operator is not authorized RVR 500 the POI will not
  select RVR 500 in the OPSS. If the OPSS is not available the POI
  should delete subparagraph b(3), & b(4) from the word boilerplate.]
(3) Touchdown zone RVR 500 (beginning of takeoff run), mid RVR 500,
  and rollout RVR 500, provided all of the following visual aids and RVR
  equipment are available.
(a) Operative runway centerline lights (CL).
(b) Runway centerline markings (RCLM).
(c) Operative touchdown zone and rollout RVR reporting systems serving
  the runway to be used, both of which are controlling, or three RVR
  reporting systems serving the runway to be used, all of which are
  controlling. However, if one of the three RVR reporting systems has
  failed, a takeoff is authorized, provided the remaining two RVR values
  are at or above the appropriate takeoff minimum as listed in this
  subparagraph.
(4) At foreign airports which have runway lighting systems equivalent
  to U.S. standards, takeoff is authorized with a reported touchdown
  zone RVR of 150 meters, mid RVR of 150 meters, and rollout RVR of 150
  meters. At those airports where it has been determined that the runway
  lighting system is not equivalent to U.S. standards, the minimums in
  subparagraphs a(1) or (2), as appropriate, apply.
c. Takeoff Guidance System, If Applicable. If the certificate holder
  is authorized to use takeoff minimums based upon the use of takeoff
  guidance systems, the minimums will be specified for the aircraft
  listed in the Table 1 below. The certificate holder shall conduct no
  other takeoffs using these takeoff minimums. If subparagraph c is not
  authorized, N/A will be annotated in each of the columns in the table.
(1) Special provisions and limitations.
(a) Operative high intensity runway lights (HIRL).
(b) Operative runway centerline lights (CL).
(c) Serviceable runway centerline markings (RCLM).
(d) Front course guidance from the localizer must be available and
  used (if applicable to guidance systems used).
(e) The reported crosswind component shall not exceed 10 knots.
(f) Operative touchdown zone, and rollout RVR reporting systems
  serving the runway to be used, both of which are controlling, or three
  RVR reporting systems serving the runway to be used, all of which are
  controlling. However, if one of the three RVR reporting systems has
  failed, a takeoff is authorized, provided the remaining two RVR values
  are at or above the appropriate takeoff minimum as listed in this
  subparagraph.
(g) The pilot-in-command and the second-in-command have completed the
  certificate holders approved training program for these operations.
(h) All operations using these minimums shall be conducted to runways
  which provide direct access to taxi routings which are equipped with
  operative taxiway centerline lighting which meets U.S. or ICAO
  criteria for CAT III operations; or other taxiway guidance systems
  approved for these operations.
(2) The certificate holder is authorized to use the following takeoff
  minimums for the airplanes listed below.
Table 1 (N/A = Not Authorized) Airplane M/M/S Lowest Authorized RVR
  Required Takeoff Guidance System
[NOTE: If an operator is not authorized pilot assessment the POI will
  not select this statement in the OPSS. If the OPSS is not available
  the POI should delete subparagraph d in its entirety from the word
  boilerplate.]
d. Pilot Assessment of RVR for Takeoff (if applicable). In
  circumstances when the touchdown zone RVR reporting system has failed,
  is inaccurate, or is not available, the certificate holder is
  authorized to substitute pilot assessment of equivalent RVR for any
  touchdown zone RVR report required by this operations specification
  paragraph provided that:
(1) The pilot has completed the FAA-approved training program for
  visibility assessment in lieu of RVR, and
(2) Runway markings or runway lighting is available to provide
  adequate visual reference for the assessment.


text:
What aircraft had the first pilot-assisted controls?
This question about regulations regarding hydraulic flight controls got me thinking about the history of hydraulic or pilot-assisted controls. As aircraft get larger the control surfaces must grow proportionally but it seems that the forces required to move those surfaces may grow at a non-proportional rate. That means at some point they had to switch from a pure cable/pulley system to an assisted system.
What is the first aircraft to use an electrical/mechanical/hydraulic system to assist the pilot with the control surfaces? I'm mostly interested in an answer from a commercial aircraft standpoint.

It was the Lockheed Constellation and the P-80, both introduced in 1943. The DC-3 had hydraulic flaps, but the Connie was the first to have hydraulic flight controls.

The DC‐3 had wings flaps powered by hydraulics (1934). But it wasn’t until the early 1940s that hydraulics were used to power the primary flight control surfaces on the Lockheed Constellation and P‐80 (first US Jet Aircraft).

Source: A History of Aviation Actuation, Control and Fluid Power (PDF)
Also in 1943, the Lockheed P-38J-25-LO version of the WWII fighter aircraft was fitted with hydraulic boosted ailerons.
Source: Lockheed P-38J Lightning, Joe Baugher

The Bell P-59 predated the P-80 as the first US jet. However, if you describe the P-80 as the first operational US jet that would, I think, be correct since though a number of P-59s were built, they never saw combat.

@Terry Thanks. I'd qualify the statement, but it's part of the source quotation.

Which was the first fly-by-wire aircraft?

@Firee  AFAIK it was the Airbus A320


text:
FAR 121.577 and first class drinks
Some airlines offer drinks for first class before departing. Would this violate 121.577(a)?
To clarify, (b) discusses tray tables but assume for this question the tray table is up.
According to FAR:

§ 121.577 Stowage of food, beverage, and passenger service equipment during airplane movement on the surface, takeoff, and landing.

(a) No certificate holder may move an airplane on the surface, take off, or land when any food, beverage, or tableware furnished by the certificate holder is located at any passenger seat.

My guess is (due to the exclusiveness of "first class") that the ones to complain (apart from the crew) would be the first class passengers themselves. Obviously unlikely.

Offering drinks while at the gate is not a violation, but presumably they would need to suspend service and collect any remaining beverages before pushback to be in compliance.

Typically first class passengers will be the first to board the aircraft. The entire boarding process can take 20 to 30 minutes until the plane is ready to go. Airlines don’t usually have large glasses so if it takes 30 minutes to drink a few ounces of orange juice and there’s something wrong with you.

What prompted the question was a couple I had dinner with was gushing about 1st class champagne during takeoff. I expected the answers to point out a loophole but apparently some flight staff is more lenient with the rules!

Not much can be concluded from one data point, especially an anecdotal story by a couple claiming they were served champagne during takeoff. Note that flight attendants are seated and strapped in during the takeoff roll so we already know that this did not literally happen. As for what truth they were possibly stretching a bit that's hard to say. Not everyone who flies is paying that much attention to what the airplane is doing at every moment.

It has been my experience that the FAs often collect first class beverages, but not always. I've noticed that if a passenger is in the middle of their beverage and don't look like they're going to spill it, the FA might look the other way and let them keep sipping through takeoff. To @StevePemberton's point, though, this is anecdata.


text:
How does a standby ADI remain accurate when flying over the curved earth?
How does a standby attitude directional indicator remain accurate when flying for many hours over the curve of the earth? While maintaining level flight, wouldn’t the pilot see an apparent movement of the attitude indicator in relation to curvature he/she is flying over?

Those answers don't address his specific question.  The answer to his question is that "level" isn't level as in a constant plane through space.  "Level" on earth is perpendicular to the center, or aligned with a spherical plane about the earth at the airplane's distance from the center.

@JohnK A gyroscopic AI has an erection mechanism, which continuously corrects the AI to be upright based on the local level, or downward acceleration vector. How does that not answer this?

The explanation of the erection mechanism covered correcting for precession drift, and if you think it through it would also explain why the gyro doesn't remain on a constant plane but is continuously realigned toward the center of the earth but I don't think that aspect was explicitly covered in the answer.  Maybe I missed it when I read them.


text:
Which type of jet leaves black trail at cruising altitude?
I was recently travelling to Morocco, and as I was sitting by the window, at some point mid-flight I noticed another jet travelling in opposite direction at our altitude. The reason I noticed it easily, was that it was leaving very dark, solid, nearly close to black colour trail. It definitely was at cruising altitude, as after that we were still flying for about 1.5 hours before landing. I just can guess that it was small-ish jet, as height of its body appeared nearly the same as diameter of the trail. I couldn't see much details any way, as it was about a mile from us.
Does the black trail indicates fuel inefficiency of an engine, and that could be on of the old military jets?

I used to fly the North Atlantic MNPS airspace a lot. If in the clear during daylight we noticed a small black smudge seemingly directly in front of us, we knew from experience that it was likely another aircraft 1,000 feet off our altitude going in the opposite direction leaving a contrail. At first we wouldn't be able to see the aircraft as it would be too small to be seen head on. Eventually we would see the aircraft as it flashed by us, usually a little bit right or left, either above or below. 1,000 feet doesn't look like much at altitude.Contrails white from below, look black head on.

@Terry I think this should be the answer rather than the linked duplicate - the chances of unfamiliar ambient lighting at altitude are much higher than a smoky jet, these days.

@Sanchises -- absolutely spot on! The close-as-duplicate vote is incorrect. Voting to reopen!

That could easily be a military jet, or it could be an older type passenger jet. The old jet engines had inefficient fuel injectors and simply used a lot of them, creating a higher fuel-to-air ratio which results in black smoke from carbonised fuel. There is only a short time to mix the fuel with the air under pressure in the combustion chamber, and modern day engines pre-mix the fuel with air before injecting.
Olden days jet engines also used water injection in times of high demanded thrust, creating more black smoke due to a cooler combustion chamber, but since the aircraft you saw was in cruise it would not be in a water injection flight phase.
So any older type of jet engine could have caused the black smoke you saw. Could have been an old DC-9 or even a B-52 :)

Wait a minute...what?


text:
What constitutes a flight review for the purposes of eligibility for a remote pilot certificate under 14 CFR 107.61(d)(2)?
An applicant for the Remote Pilot Certificate who already holds a pilot's license can forgo the knowledge test required by 14 CFR 107.61(d)(1) if they have a current flight review. The regulation states that an applicant must be able to demonstrate aeronautical knowledge by satisfying one of the following conditions:

14 CFR 107.61(d)
(1) Pass an initial aeronautical knowledge test covering the areas of knowledge specified in §107.73(a); or
(2) If a person holds a pilot certificate (other than a student pilot certificate) issued under part 61 of this chapter and meets the flight review requirements specified in §61.56, complete an initial training course covering the areas of knowledge specified in §107.74(a) in a manner acceptable to the Administrator.

14 CFR 61.56 specifies that a flight review is:

(a) Except as provided in paragraphs (b) and (f) of this section, a flight review consists of a minimum of 1 hour of flight training and 1 hour of ground training.
[...]
(b) Glider pilots may substitute a minimum of three instructional flights in a glider, each of which includes a flight to traffic pattern altitude, in lieu of the 1 hour of flight training required in paragraph (a) of this section.
[...]
(f) A person who holds a flight instructor certificate and who has, within the period specified in paragraph (c) of this section, satisfactorily completed a renewal of a flight instructor certificate under the provisions in §61.197 need not accomplish the one hour of ground training specified in paragraph (a) of this section.

Are these definitions to be understood as the definition of a flight review, or might the following flight review exemptions also count for the purposes of §107.61(d)(2)?

(d) A person who has, within the period specified in paragraph (c) of this section, passed any of the following need not accomplish the flight review required by this section:
(1) A pilot proficiency check or practical test conducted by an examiner, an approved pilot check airman, or a U.S. Armed Force, for a pilot certificate, rating, or operating privilege.
(2) A practical test conducted by an examiner for the issuance of a flight instructor certificate, an additional rating on a flight instructor certificate, renewal of a flight instructor certificate, or reinstatement of a flight instructor certificate.
(e) A person who has, within the period specified in paragraph (c) of this section, satisfactorily accomplished one or more phases of an FAA-sponsored pilot proficiency award program need not accomplish the flight review required by this section.

For the purpose of initial certification under §107(d)(2), is a flight review to be understood strictly as the training defined by 14 CFR 61.56 (a), (b), or (f), or do the exemptions to the requirement for a flight review—14 CFR 61.56 (d) or (e)—also count as a flight review?

Note that the requirement is to do it "in accordance with 61.56", and not "in accordance with 61.56(a), (b), or (f)".  They basically want the pilot to be "current" with their flight review, and that can be accomplished in any of the normal ways.

@Lnafziger I agree with you that this is likely the spirit of the regulation, but it does not merely say the requirements of 61.56. It says the flight review requirements of 61.56, hence my question.

Well, the title of 61.56 is flight review, hence my comment.  ;-)

The intent is not a flight review per se, but rather having demonstrated adequate aeronautical knowledge (to waive the written test).  That being the case, the CFI exemption for the one hour ground would suggest that the CFI would be exempt from the flight review requirement, but that is not how the regulation is written.

You have to take into account the intent of the regulation.  I think the regulations intent is to ensure the pilot has been evaluated on his knowledge within the previous two years by either a CFI or examiner.
With that in mind, a flight review by a CFI or passing a practical test by an examiner satisfies the requirement for the remote operator to take the full initial knowledge test.

From the preamble to the Part 107 final rule.

The FAA proposed that a certificated remote pilot must also pass a recurrent aeronautical knowledge test every 24 months. Like the flight review requirement specified in §61.56, the recurrent knowledge test provides the opportunity for a remote pilot’s aeronautical knowledge to be reevaluated on a periodic basis. The FAA adopts this provision as proposed, with one change. As discussed in III.F.2.i, the FAA exempts part 61 pilot certificate holders from the requirement to complete recurrent knowledge tests as long as they satisfy the flight review requirements of §61.56 and complete an online training course every 24 months

Page 6 paragragh g.

The FAA agrees with commenters who suggested that requiring part-61- certificated pilots who satisfy the flight- review requirements of §61.56 to take an initial or recurrent knowledge test is unduly burdensome. Through initial certification and subsequent flight reviews, a part-61-certificated airman is required to demonstrate knowledge of many of the topic areas tested on the UAS knowledge test. These areas include: Airspace classification and operating requirements, aviation weather sources, radio communication procedures, physiological effects of drugs and alcohol, aeronautical decision-making and judgment, and airport operations. Because a part 61 pilot certificate holder is evaluated on these areas of knowledge in the course of the part 61 certification and flight review process, reevaluating these areas of knowledge on the initial and recurrent knowledge tests conducted under part 107 would be needlessly duplicative.

Page 13 paragraph I

I wonder if completing a phase of the FAAST program, in accordance with §61.56(e) would also count? These programs seem less comprehensive.

Completion of a FAAST wings phase counts as a flight review and will qualify for this regulation as well.

According to §61.56(d) it does not count as a flight review, but exempts the pilot from the requirement for a flight review: "need not accomplish the flight review required by this section".


text:
How are weather-related limits on arrival capacity determined?
Most airports in Europe have the following traffic controls imposed during adverse weather conditions. I wonder whether these capacity limits are determined by airport operator's experience, or if there are any special algorithms?

ATC has to keep planes a minimum distance apart, and that distance increases as weather gets worse. You could fairly easily calculate from the required spacing in each case to get an expected arrival rate, but the real world never works exactly as planned. The numbers in that table have almost certainly been "adjusted" to make them agree with experience.


text:
What is this USAF transport aircraft from possibly the 50-60s?
I came across the following image (scan of a photograph) in an archive of photographs related to the 1962 Sino-Indian War.

Which particular aircraft could this be?
Update: This answer identifies it as belonging to 322d Airlift Division.

Please provide a source for your image

@TomMcW, it's a scan of a photograph...

Is the original photo clear enough to make out the badge that’s cut off to the upper left of the door

@TomMcW, unfortunately I don't have access to the original photographs now. I actually got the scanned images and optimised them. There was minimum cropping so most probably the full badge is unavailable...

It is indeed a C-130A. The large tail numbers indicate it's from the late 50's or early 60's. In the late 60's, the USAF went with smaller numbers forward of the passenger door. Here's a similar a/c image from C-130.net

Further searching of the C-130 Aircraft Database shows the only "014" to be be s/n 55-0014. The history shows it was assigned to the 40th TAS which was part of the 322nd AD.
In 1968 it was converted to an AC-130A gunship. It is currently on display at the Museum of Aviation at Robins AFB.

Those camels on the side of the plane...


text:
Why does the F-111 have a capsule ejection system rather than a conventional system?
Following on from the questions F-111 emergency landing with no wheel; what is done to reduce risks when loosing a wheel? and
Are there any known incidents of ejections by capsule? What are the survival chances?
I wondered, what is the reason for the ejection capsule on the F111?
It doesn't fly particularly high or fast (compared to aircraft with conventional ejection seats). The only reason I can think of is that the pilots sit almost side-side and it would presumably be tricky to fire the first seat without seriously inconveniencing the remaining crew member.
Are there any side-side aircraft with ejection seats?

The A-6 Intruder has side-by-side seating and conventional ejection system.

I wouldn't call Mach 2.5 "not particularly fast" - quite the opposite!

And that's not even the Aardvark's top speed, either, Peter.  The aircraft never had one as the pilot could destroy it from airframe heating before it stopped accelerating at full throttle.

The reason the F-111 has an ejection capsule is pretty weird in itself- its there because USN wanted it.
In 1960, USAF asked for an aircraft capable of supersonic flight for 400 miles, and capable of operating from short/unprepared fields and capable of crossing Atlantic unrefuelled through Specific Operational Requirement (SOR) 183. At the same time, USN was trying to develop a fleet defender for its carrier groups which had high loiter time (> 6hrs) and can detect/launch missiles at incoming bombers and sea skimming missiles at over 100 miles. To this extent, the Douglas F6D Missileer was proposed, which got cancelled in 1961.
Unfortunately for USAF (and lot of others), US SecDef Robert McNamara decided that both these requirements could be met by the same aircraft- actually, the only things they agreed about were that the aircraft would have swing-wing, have two seats and have two engines.
The USAF wanted tandem seating, while the USN wanted a side-by-side seating for improving crew co-ordination sharing the large radar display to launch missiles (like the A-6 Intruder, which had side by side seating, but conventional ejection seats). The reason the ejection capsule was included was that USN believed that it would give better chances of survival in case of ejection over sea (where it was to function as a life raft) and in high speed ejection. The USAF hated this as it increased the weight by over 500 lb, affecting performance.
In fact, the Boeing proposal included conventional ejections seats, which was required to be changed into a capsule (and was selected before McNamara intervened and selected the other one). In the end, USN escaped from the project (ironically due to weight and performance issues), while the USAF and others got stuck with the ejection capsule, which they never wanted in the first place.

My response is  that I was a design engineer on the F-111 project with responsibilities associated with the design and test of the module. Traditional ejection seat concept provided no survivable protection for escape at the upper (higher) speeds and altitudes of the operational envelope of the F-111. This is true for tandem or side-by-side seating configurations. The only significant design constraint imposed by the Navy was to be able to separate up to 30 feet under water. Interestingly, the control stick could be converted into a “bilge” pump handle in event of water landing. The first use of the escape module was from a test aircraft having lost hydraulics in the flight control system. This occurred over Bowie, Texas.  The pilot scratched his finger climbing through a barbed wire fence! The only injury!

It has to do with the realities of a supersonic ejection at high altitudes, which is usually fatal for unprotected aircrews, both from bodily trauma from exposure to a supersonic slipstream and the extreme low temperatures and pressures which would be encountered at typical cruise altitudes.
The United States invested in increasingly faster supersonic bombers in the 1950s and 60s in order to thwart conventional defences and interceptors operated by the east bloc, so the realities of Mach 2 or Mach 3 flight demanded these kind of enclosed and pressurized escape systems in the event of an inflight emergency or enemy attack.  But the realities of modern Warsaw Pact IADS using radar guided missiles made supersonic and easily detected bomber fleets an impractical investment for strategic nuclear delivery.  With the return to the subsonic flight envelope and lower operational altitudes made conventional ejection seats a much more mature and realistic option for an escape system.
A good example of this was the Rockwell B-1A, which was to have used an large four man escape capsule similar to the F-111's prior to its cancellation by the Carter Administration.  It's successor, the B-1B which was optimized for slower and low level penetration abandoned the escape capsule for the mature and established McDonnell Douglas ACES II ejection seats at each crew station.
Additionally, escape capsules are large, heavy, complex pieces of equipment, not to mention expensive.  The F-111's escape capsule cost as much as a completed F-86 SaberJet.  Complexity increases the number of failure modes and risk of failure during emergency use exponentially, requiring more maintenance, etc.
Curiously one high altitude, high speed cruiser, the Lockheed A-12/SR-71, used conventional ejection seats throughout its career albeit requiring the crew to suit up in full pressure suits during the flight.  I do not believe that the seats were intended for use at supersonic speeds, leaving no means of escape for the crew during this regime of flight.  This was also true of the North American X-15, a Mach 6 research aircraft where an ejection at cruise altitude and speeds would have certainly proved fatal.

Are there any side-side aircraft with ejection seats?

Yes.  Multiple aircraft with this cockpit configuration used ejection seats including the B-1, B-52, B-2, A-6, OV-1, and T-37.